slartabartfast
Some interesting studies that suggest monkeys lack the capability to follow the beat/meter of rhythmic auditory stimuli (rhythmic entrainment), a capability shared by humans and some bird species. The ability to follow or extract an underlying beat from rhythmic stimuli is a different psychoacoustic process than the ability to recognize variation in patterns of time and duration i.e. rhythms, and further links the ability to language.
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0051369
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3894452/
I kinda doubt that monkeys (or people) only had the ability to catch one thing, and not the other. Going as far back as Greek Theater, done in the early morning so the voice would not carry away, already suggested that other sounds/voices/song were also listened to and danced to.
I kinda think that the "rhythmic" thing was likely the first thing to get "written" down in some form, so the piece of music would make sense, otherwise, everyone would be different, thus, it makes sense to suggest that it was what came first.
That is not to say that it was not "there" and that no one could pick up on it, and change things, and augment it into something else, and what we eventually think became war chants and various other determinations that have defined music for a couple thousand years.
There is so much to study in that area, it's not funny. We still don't really know a whole lot about it, and much of it was erased by religions over the past several thousand years, because these things were not considered "proper" and were also "banished" many times, as "evil" and a part of the devil's doing.
Heck, so was coffee, one time as a papal decree!
Peter Brook, has spent many years, working/defining the stage/public relationship and his studies are monumental and although possibly influenced by Gurdgieff, they are still ... wonderful to listen to ... you never knew such a slight detail was so important! And a lot of this, may have come from the very first "sound" that we turned into "music" ... which we still have not been able to define very well.